"I went to the Depot and picked up a 4'x8' sheet of 2" Styrofoam insulation and 15' of Velcro tape for about $50 and built a 24"x28"x20", collapsible, fermentation room. I control the temp by putting in a gallon milk jug filled with water. I freeze the jug to cool and fill it with hot water to warm my fermentor. When I don't need it, I just break it down and throw it on a shelf.

There's enough room in the cooler for a 6.5 gallon bucket, blow off collector, and the gallon jug. By rotating two frozen jugs, I can keep the temp at 65° when it's 85° outside. "

If you're looking to control your fermentation temperature cheaply, this is the way to go. You could get better efficiency if you make it a permanent structure by gluing and sealing the seams.

It depends on what you mean by low cost... the only reason I say that is that you can do a lot of really low-cost methods that won't cost you anything. For example, if you're looking bring temps down a little bit you can just put your carboy in some kind of containter with a some water in the bottom of it and then wrap a wet towel around the carboy with the towel dipped in the container a little bit (if that all made sense). The towel will draw water and as it evaporates, it'll coolt he carboy down quite a bit...

but again... you're not going to need that for 68 degrees.... that's a great temp for a majority of beers and if you want to lager... you're going to need something more substantial and will need some sort of actual chamber.

The way I did it... and it was pretty cost effective... is look on Craigslist for a free refridgerator. They are around all the time. Grab a free fridge, go to home depot and buy a cheap thermostat and then find someone who can wire it up for you (if you can't do it yourself).

I have two cheap thermostats (about 20 bucks each) in a fridge that are wired one for cold and one for heat.... and then I have a plug coming off of the "heat" thermostat that I can plug a reagular heating pad into.

If I am lagering, I turn "cool" thermostat down to my temp and the fridge kicks on and cool it down. If I want hotter ferm temps, I turn the "heat" thermostat up and the heating blanket kicks on, warming the whole thing.

You can also do what I did. I had an old microwave cart with a cabinet that was large enough to hold a fermenting bucket with the air lock. I lined the entire inside with styrofoam sheets, and placed an old ceramic heater inside. I stuck a meat thermometer into the cabinet, with the guage sticking out so I can see it. I adjusted the temperature on the heater so that it would maintain 68 degrees in the cabinet. It worked like a charm, as the ambient temp of the room was well below 60 degrees during the winter and early spring. The amber ale had a good fermentation (4.5% alcohol), and had no off flavors at all with just a 2 week ferment.

What are you brewing? Some beers benefit more from higher fermentation temperatures, some from lower. Remember that fermentation itself gives off heat. Your fermenter will be 5° to 10° warmer than the ambient temperature, at least for the first three or four days. A beer that you want to keep crisp and clean, pitched with a neutral yeast (1056, WLP001, US05, et al), would do very well in your basement. Pitch your yeast at 65° to 70° and put the bucket in the basement. By the time the wort starts to cool, fermentation will have begun. A beer that benefits from more yeast character, a wit or ESB, for example, would be very happy upstairs. If that were the case, I'd probably cool the wort to 60° or so, pitch the yeast, and let it come up to temperature as the yeast goes to work, but that's just me.

As has been noted, you can control temperatures fairly well with inexpensive tools. I use a bus tub, the kind used to clear tables in restaurants ($5 at your local restaurant supply), filled with water to keep my fermenter cool. Changing out a couple of frozen water bottles a day keeps the fermenter at 62° to 65° even in 75° ambient temperatures.